Display screen or portion thereof with a transitional mixed reality graphical user interface



FIG. 1 is a front view of a display screen or portion thereof with a transitional mixed reality graphical user interface showing a first image in a sequence of a design; and,

FIG. 2 is a front view of a display screen or portion thereof with a transitional mixed reality graphical user interface showing a second image in the sequence of the design.

The appearance of the transitional graphical user interface transitions sequentially between the images shown in FIGS. 1-2. This process or period in which one image transitions into another forms no part of the claimed design.

The outermost broken lines show a display panel or portion thereof that forms no part of the claimed design. The broken line showing of the interior space and furniture is included for the purpose of illustrating unclaimed mixed reality environmental structure, and the broken line showing of text and features formed by circles is included for the purposes of illustrating portions of the graphical user interface that form no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with a transitional mixed reality graphical user interface, as shown and described. 